1. Field of the Invention
The invention relates to a steam power plant with retrofit kit and to a method for retrofitting a steam power plant.
2. Discussion of Background
Power plants with a conventional water/steam cycle are known from the prior art. Known steam turbine installations are formed by a steam turbine set including condensation installation, connecting pipelines and auxiliary devices. The steam turbine set generally comprises multistage steam turbines. The steam turbine set drives a working machine, which in the case of a power plant is formed by a generator. Large steam turbine installations operated with fossil fuels usually employ a process which includes reheating.
A steam power plant with reheating of this nature is diagrammatically depicted in FIG. 7. In this case, condensate or boiler feedwater is heated to the desired steam temperature in a steam boiler 1 including superheater 2. The live steam temperature is generally approximately 520° C. to 565° C., and the live steam pressure is approximately 120 bar to 200 bar. Via live steam valves 3, the steam passes into a high-pressure turbine 4, where the pressure gradient is converted into mechanical energy before the steam, at the outlet, is divided into a stream which is fed to a high-pressure feedwater preheater 21 and a stream which is fed to a reheater 5. The steam which is fed to the high-pressure feedwater preheater 21 is also referred to as bleeder steam for feedwater preheating and is used to heat the feedwater by means of heat exchangers. As has already been mentioned, the second part-stream passes via a reheater 5 and collecting valves 6 into an intermediate-pressure turbine 7, where the pressure and temperature are typically 30 to 40 bar and 520° C. to 565° C. Bleeder steam for the feedwater preheating likewise passes from the intermediate-pressure turbine 7 into high-pressure feedwater preheaters 19 and 20 or directly into a feedwater tank 17 connected to a boiler feed pump 18. The other part of the flow of steam, which is also referred to as working steam, passes into a low-pressure turbine 8, from where the working steam which emerges flows into a condensation installation 11 designed as a condenser, in which the steam is condensed by means of a heat exchanger through which cooling water flows. The condensate is preheated by means of, for example, two low-pressure feedwater preheaters, indicated in this figure by reference numerals 15, 16, and is fed to the feedwater tank 17 with the aid of a condensate pump 13. The preheating in the low-pressure feedwater preheaters 15, 16 is carried out using bleeder steam from the low-pressure turbine 8. Steam power plants which also remove additional bleeder steam at elevated pressure at the high-pressure turbine 4 for an additional feedwater preheating stage are also known. The high-pressure turbine 4, the intermediate-pressure turbine 7 and the low-pressure turbine 8 are in this case generally arranged on a common shaft 9, which is mounted rotatably by means of shaft bearings 12. The shaft 9 drives a rotor of a three-phase current generator 10 which is responsible for generating the current.
The service life of conventional steam power plants of this type is approximately 40 to 50 years. However, on account of their original design and the aging of components, relatively old steam power plants only achieve a moderate efficiency and therefore have an increased fuel demand, which is associated with high operating costs and emissions. Therefore, many relatively old steam power plants, even though in mechanical terms they are still functional and have by no means reached the end of their operating life, are uneconomical at producing electricity. This is true in particular in view of increased competition from markets where modern plants, including combined-cycle power plants, which have a gas turbine cycle and a steam turbine cycle, as described, for example, in DE 19542917 A1 or DE 19923210 A1, are operated.
One approach which is currently used to avoid losses of this nature is conventional retrofitting of relatively old steam power plants, in which only the steam path of the turbines is modified. For this purpose, new rotating and stationary turbine blades and vanes with an improved profile are exchanged for the old turbine blades and vanes. In general, only certain rows of blades or vanes are exchanged, while the other rows of these blades or vanes continue to operate unchanged. The result of this measure is that the power output by the steam power plant rises for the same fuel consumption with substantially unchanged steam conditions. Moreover, instead of exchanging only the turbine blades or vanes, it is also possible at the same time to exchange the entire rotor including the rotating blades and/or the stator in which the stationary vanes are arranged, and in this way to make better use of the existing steam turbine installation. A modification of this type alone does not require any major changes to the generator, the steam boiler, pipelines, condensers or buildings. The steam temperature and the steam pressure remain substantially unchanged in the event of a retrofit of this nature.
A drawback of this retrofitting measure is that the increase in output and efficiency is generally only moderate. Improving the efficiency, i.e. reducing the fuel consumption with an unchanged electrical output or increasing the electrical output with an unchanged fuel consumption, is too low, however, to greatly reduce the costs per kilowatt hour and to constitute a significantly more attractive solution in terms of achieving more competitive prices or reducing specific emissions. Consequently, the competitiveness of relatively old steam power plants can scarcely be increased to a significant degree in this way.
It is true that DE 19962386 A1 and DE 19962403 A1 disclose methods for retrofitting or converting a system which generates saturated steam with at least one steam turbine assembly, and power plants which have been retrofitted or converted using these methods. However, in this case it is proposed for a gas turbine set to be added as an addition to the steam turbine set, which is equivalent to restricting the fuel supply. Furthermore, this creates a combined-cycle installation, which is more complex to maintain than a pure steam turbine installation.